Allyl thiourea polymer with surface-modifying agent

ABSTRACT

Various acrylic acid allyl/thiourea polymers and their use as depressants in the beneficiation of sulfide minerals from ores are disclosed.

This is a division of Ser. No. 221,389, filed July 19, 1988, now U.S.Pat. No. 4,902,765.

BACKGROUND OF THE INVENTION

The present invention relates to froth flotation processes for recoveryof mineral values from base metal sulfide ores. More particularly, itrelates to new and improved sulfide mineral depressants for use inseparating or beneficiating sulfide minerals by froth flotationprocedures, and to a new and improved process for beneficiating sulfideminerals by froth flotation incorporating said depressants.

Certain theory and practice state that the success of the sulfideflotation process depends to a great degree on reagents calledcollectors that impart selective hydrophobicity to the mineral value ofan ore which has to be separated from other minerals contained therein.

Certain other important reagents, such as the modifiers, are alsolargely responsible for the success of flotation separation of thesulfide and other minerals. Modifiers include all reagents whoseprinciple function is neither collection nor frothing, but one ofmodifying the surface of the mineral so that a collector either adsorbsto it or does not. Modifying agents may thus be considered asdepressants, activators, pH regulators, dispersants, deactivators, etc.Often, a modifier may perform several functions simultaneously. Currenttheory and practice of sulfide flotation further state that theeffectiveness of all classes of flotation agents depends to a largeextent on the degree of alkalinity or acidity of the ore pulp. As aresult, modifiers that regulate the pH are of great importance. The mostcommonly used pH regulators are lime, soda ash and, to a lesser extent,caustic soda. In sulfide flotation, however, lime is by far the mostextensively used. In copper sulfide flotation, which dominates thesulfide flotation industry, lime is used to maintain pH values over10.5. The costs associated with adding lime are becoming quite high andplant operators are exploring flotation processes which require littleor no lime addition, e.g., flotation processes which are effectivelyconducted at slightly alkaline, neutral or even at acid pH values.Neutral and acid circuit flotation processes are particularly desiredbecause pulp slurries may be easily acidified by the addition ofsulfuric acid and sulfuric acid is obtained in many plants as aby-product of the smelters. Therefore, flotation processes which requirepreadjustment of pH to neutral or acid pH values using less expensivesulfuric acid are preferable to current flotation processes, whichpresently require pH readjustment to highly alkaline values of at leastabout 11.0 using lime which is more costly.

As has been mentioned above, lime consumption in individual plants mayvary anywhere from about one pound of lime per metric ton of oreprocessed up to as high as 20 pounds of lime per metric ton of ore. Incertain geographical locations, such as South America, lime is a scarcecommodity, and the current costs of transporting and/or importing limehas risen considerably in recent years. Still another problem with priorart high alkaline processes is that the addition of large quantities oflime to achieve sufficiently high pH causes scale formation on plant andflotation equipment, thereby necessitating frequent and costly plantshutdowns for cleaning.

It is apparent, therefore, that there is a strong desire to reduce oreliminate the need for adding lime to sulfide flotation processes. Inaddition, reducing or eliminating lime in sulfide ore processes willprovide other advantages by facilitating the operation and practice ofunit operations other than flotation, such as fluids handling or solidshandling, as well as the improved recovery of secondary minerals.

In general, xanthates and dithiophosphates are employed as sulfidecollectors in the froth flotation of base metal sulfide ores. A majorproblem with these sulfide collectors is that at pH's below 11.0, poorrejection of pyrite or pyrrhotite is obtained. More particularly, inaccordance with present sulfide flotation theory, the increasedflotation of pyrite at a pH of less than 11 is attributed to the ease ofoxidation of thio collectors to form corresponding dithiolates, whichare believed to be responsible for pyrite flotation.

In addition to attempts at making the sulfide collectors more selectivefor value sulfide minerals, other approaches to the problem of improvingthe flotation separation of value sulfides have included the use ofmodifiers, more particularly depressants, to depress the non-valuesulfide minerals and gangue minerals so that they do not float in thepresence of collectors, thereby reducing the levels of non-value sulfidecontaminants reporting to the concentrates. As has been mentioned above,a depressant is a modifier reagent which selectively prevents orinhibits adsorption of the collector on certain of the mineral particlesurfaces present in the flotation slurry or pulp. Prior art sulfidedepressants have generally comprised highly toxic and difficult tohandle inorganic compounds such as sodium cyanide, (NaCN), sodium hydrosulfide, (NaSH), and Nokes reagent (P₂ S₅ and NaOH). These conventionalsulfide depressants represent a number of serious problems and haveserious shortcomings attendant their use. The oft used depressants arefrequently extremely toxic and may be associated with a terrible stench.They cannot be used safely over a wide range of pH values, but insteadmust be used at high pH values, so that lime consumption problems arenot solved by their use. Moreover, the conventional inorganicdepressants are often either nonselective or when used in sufficientquantities to provide good separation, provide economicallyunsatisfactory concentrates, i.e., the yield of value minerals is toolow.

The problem facing flotation beneficiation methods today is to providevalue mineral concentrations which contain substantially reduced levelsof gangue sulfide minerals. The flotation concentrates are generallydelivered to the smelting operations without any further substantialprocessing. Large amounts of sulfur dioxide are emitted from thesmelters during the smelting of sulfide concentrates; a significantamount of SO₂ is from the gangue sulfide minerals such as iron sulfides,which invariably report to the smelters as contaminants in the flotationconcentrates. Sulfur dioxide pollution of the atmosphere has always beena serious problem because it is a major cause of acid rain, which has adevastating effect on the ecology. Despite significant advances insmelting technology, SO₂ pollution remains extremely serious.

Complex sulfide ores are an important source of many base metals andprecious metals It is quite common to find 3-5 metals in each deposit,in addition to Au, Ag and impurity elements such as Sb, As, Bi and Hg.The ore treatment method depends on the relative proportions of thedifferent metals therein, but the more widely used routes are: (a) bulkflotation of sulfides followed by separation of value sulfides, and (b)differential flotation of sulfides It is necessary to characterize eachcomplex sulfide deposit quantitatively and systematically and then toselect the economically optimum combination of process steps to suit thecharacteristics. Depressants are invariably used in all stages offlotation. Lime, sodium or zinc cyanide, zinc sulfate (often incombination with sodium cyanide), SO₂, dichromate, dextrine,hypochlorite, and ferro cyanide are some of the most commonly useddepressants.

The beneficiation criteria for treating the complex sulfide ores aremaximum value metal and precious metals (if any) recovery and minimumcontamination of the value sulfide concentrate by non-value sulfideminerals In many cases, these criteria cannot be met without seriouslysacrificing value metals production or recovery Therefore, there remainsan urgent need for flotation reagents that can selectively depressgangue sulfide minerals reporting to the concentrate and concurrentlyprovide economically acceptable recoveries of value sulfide minerals.

Unexpectedly, in view of the foregoing, it has now been discovered thatcertain synthetic polymers which contain certain functional groups arevery effective depressants for all sulfide numerals in general, and,more particularly, for pyrite, pyrrhotite, and other gangue sulfideminerals. The use of the depressants of the present invention provides asubstantial reduction in gangue sulfide minerals contamination in thesulfide minerals concentrates reporting to the smelters, therebyreducing the adverse environmental impact of SO₂ emissions caused bysmelting operations in the industry. It has also been discovered thatthe instant polymers unexpectedly depress one or more value sulfideminerals in the presence of other value sulfides or non-sulfides underappropriate dosage and/or other operating conditions.

BACKGROUND OF THE INVENTION

The copolymerization of allyl thioureas with an acrylic acid has notbeen disclosed in the prior art. Allyl thioureas have, however, beencopolymerized with other materials such as sulfur dioxide (U.S. Pat. No.3,386,972) and vinyl chloride (U.S. Pat. No. 3,012,010). Thesecopolymerizations are not suggestive, however, of the copolymers of thepresent invention.

Additionally, U.S. Pat. Nos. 2,832,755; 2,837,499 and 2,858,295 disclosethe copolymerization of vinyl thioureas with unsaturated comonomerswhile U.S. Pat. No. 3,671,492 teaches the copolymerization of thioureassuch as N-vinylethylene thiourea with unsaturated monomers. None ofthese references, however, teach the production of polymers fallingwithin the structure set forth hereinbelow and all of the above-citedreferences fail to teach the use of allyl thiourea copolymers as adepressant in the recovery of mineral values from ores.

A recent pending application, Ser. No. 182,681, filed Apr. 18, 1988,discloses and claims copolymers of acrylamide and allyl thiourea andtheir use in the recovery of mineral values form ores, however, noacrylic acid based copolymers void of an acrylamide, are disclosedtherein.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, new and improved sulfidemineral depressants are provided in the form of polymeric compositions,said compositions comprising a polymer comprising:

(i) x units of the formula: ##STR1## (ii) y units of the formula:##STR2## (iii) z units of the formula: ##STR3## wherein R is hydrogen orC₁ -C₄ alkyl; each R¹ and R², individually, is hydrogen, a C₁ -C₄ alkylgroup or an aryl group, each R³, is hydrogen, a C₁ -C₄ alkyl group or anaryl group, M is hydrogen, an alkali metal, ammonium or C₁ -C₄ alkylammonium, Z represents the polymerization residue of any monomer exceptan acrylamide copolymerizable with units X and Y, x represents aresidual mole percent fraction, preferably 10-90%, y is a mole percentfraction ranging from about 1.0% to about 49%, preferably 5-30%, z is amole percent fraction ranging from about 0% to about 49%; preferably0-30%, and the molecular weight of the polymer ranges from about 1,000to about 1,000,000.

In preferred embodiments, the polymeric compositions comprise polymerswithin the scope of the above definition which comprise as the Y units,monomeric units wherein R¹, R² and R³ are all hydrogen.

The new and improved compositions of the present invention may beprepared by known polymerization methods whereby the acrylic acidcomponent X is co-polymerized with the thiourea component Y and,optionally, with comonomer unit Z. Examples of suitable polymerizationprocedures are set forth in U.S. Pat. Nos. 3,002,960 and 3,255,142,hereby incorporated herein by reference. More particularly, the monomersmay be copolymerized at 30-100° C., preferably 45-65° C., with peroxide,VAZO® type and redox catalysts using, as the reaction arena, water, C₁-C₄ alcohols, DMF, DMSO, N-methyl pyrolidone, dioxane, etc.

More particularly, the polymers of this invention comprise as the (X)units, those derived from acrylic acid per se, methacrylic acid oralkali metal, ammonium or C₁ -C₄ alkyl ammonium, e.g., mono, di, tri andtetramethyl ammonium salts of acrylic acid and methacrylic acid,ethacrylic acid etc.

The (Z) units of the polymers defined above exclude acrylamide monomerssuch as acrylamide per se, alkyl acrylamides and N-substitutedacrylamides and generally comprise monomers such as acrylonitrile,styrene, cationics such as diallyl dimethyl ammonium chloride,methacrylamidopropyl trimethylammonium chloride, acrylamidopropyltrimethylammonium chloride, dimethylaminopropyl methacrylamide,dimethylaminoethyl acrylate or methacrylate and their quaternary salts,2-acrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, acrylic,methacrylic or maleic acids, their alkali metal e.g., sodium orpotassium, or ammonium salts, and alkyl esters thereof and the like.

The (Y) units of the polymers defined above are derived from thioureaderivatives such as allyl thiourea, N-allyl-N'-methyl thiourea,N-allyl-N'-benzoyl thiourea, N-allyl-N-methyl-N',N'-dimethyl thioureaand the like. These novel polymers may be used in flotation processesfor important separations; for example, copper sulfides from molybdeniteby depressing the former; lead and copper sulfides from pyrite andsphalerite by depressing the latter; pentlandite from pyrrhotite bydepressing the latter; copper sulfides or sphalerite from pyrite bydepressing the latter, etc. at dosages ranging from about 0.001 kg/tonto 1.0 kg/ton on an active solids basis.

In another aspect, the present invention provides a new and improvedmethod for the beneficiation of value sulfide minerals from sulfide oreswith selective rejection of gangue sulfide minerals, said methodcomprising:

(a) providing an aqueous pulp slurry of finely divided, liberation-sizedore particles:

(b) conditioning said pulp slurry with an effective amount of asynthetic depressant, a sulfide mineral collector and a frothing agent,said synthetic depressant comprising a polymer comprising:

(i) x units of the formula: ##STR4## (ii) y units of the formula:##STR5## (iii) z units of the formula: ##STR6## wherein R is hydrogen orC₁ -C₄ alkyl, each R¹ and R² is, individually, hydrogen, C₁ -C₄ alkyl oran aryl group, R³ is hydrogen, a C₁ -C₄ alkyl group or an aryl group, Mis hydrogen, an alkali metal, ammonium or C₁ -C₄ alkyl ammonium, Zrepresents the polymerization residue of any monomer, except anacrylamide, copolymerizable with units X and Y, x represents a residualmole percent fraction, preferably 1-90%; y is a mole percent fractionranging from 1.0 to about 49%; preferably 5-30%; z is a mole percentfraction ranging from about 0% to about 49%; preferably 0-30% and themolecular weight of said polymer ranges from about 1000 to about1,000,000; and,

(c) collecting the value sulfide mineral by froth flotation procedures.

The new and improved method for beneficiating value sulfide minerals byfroth flotation procedures employing the synthetic depressants inaccordance with this invention provides excellent metallurgical recoverywith significant improvements in grade. The novel sulfide mineraldepressants are effective over a wide range of pH and dosages Thedepressants are compatible with available frothers and sulfide mineralcollectors and may be readily incorporated into any currently operatingsystem or facility. Moreover, use of the polymeric sulfide mineraldepressants can significantly reduce SO₂ emissions from smeltingoperations by reducing the amount of gangue sulfide minerals whichremain in the value sulfide concentrate to be smelted.

The present invention is directed to the selective separation ofsulfides, for example, gangue sulfides, from copper ores,copper-molybdenum ores, complex sulfide ores, etc. containing lead,copper, zinc, silver, gold, etc., nickel and nickel-cobalt ores, goldores and gold-silver ores and to facilitate copper-lead, lead-zinc,copper-zinc separations, etc.

The following examples are set forth for purposes of illustration onlyand are not to be construed as limitations on the present invention,except as set forth in the appended claims All parts and percentages areby weight unless otherwise specified.

EXAMPLE 1

To a suitable 4-neck vessel equipped with a mechanically driver stirrerand a condenser, are added 41.0 parts of 36.6% allyl thiourea in 1:1isopropanol and water, and 150 parts of water. The pH is adjusted toabout 5.0 with 50% sulfuric acid. The vessel is heated to 55° C., and 22parts of ammonium persulfate (20%), 21 parts of sodium metabisulfite(17%), and 164 parts of acrylic acid, neutralized (pH 7.0) withconcentrated ammonium hydroxide, are metered in separately. The monomerfeeding time is 90-100 minutes and redox catalyst feeding time is180-200 minutes. The polymerization is continued three additional hoursafter the addition of the redox catalyst. The finished product has abulk viscosity of 300 cps and an intrinsic viscosity of 0.36.

EXAMPLE 2

The procedure of Example 1 is again followed except that2,2'-azobis(2,4-dimethylvaleronitrile) (ABDV) catalyst is used. Acopolymer is obtained. Analysis of this copolymer shows that thecopolymer contains about 7.6 mole percent allyl thiourea.

EXAMPLES 3-9

The procedures of Examples 1 and 2 are again followed, i.e., eitherammonium persulfate (APS) or ABDV is used to initiate thepolymerizations. The compositions prepared are shown in Table I, below.Mercaptoethanol is used as a chain transfer agent.

                                      TABLE I                                     __________________________________________________________________________    (Weight %)                                                                    X units      Y units  Z units                                                 Example                                                                            R;  M   R.sub.1 ;                                                                        R.sup.2                                                                             R.sup.3       Catalyst                                  __________________________________________________________________________    3    H  H(80)                                                                              H  CH.sub.3                                                                            H(20)                                                                                --     ABDV                                      4    H  Na(70)                                                                             H  (CH.sub.2).sub.2 OH                                                                 H(15)                                                                              DADMAC.sup.2 (15)                                                                      ABDV                                      5    CH.sub.3                                                                         Na(80)                                                                             H  2-OH ethyl                                                                          H(15)                                                                              NAPTAC.sup.3 (5)                                                                       ABDV                                      6    CH.sub.3                                                                         H(90)                                                                              H  n-butyl                                                                             H(2) DMAEMMC.sup.5 (8)                                                                      ABDV                                      7    H  NH.sub.3 (75)                                                                      H  n-phenyl                                                                            H(5) APTAC.sup.4 (20)                                                                       ABDV                                      8    H  K(45)                                                                              H  H     CH.sub.3 (45)                                                                      EA.sup.1 APS                                       9    H  H(50)                                                                              CH.sub.3                                                                         CH.sub.3                                                                            H(10)                                                                              MAPTAC.sup.3 (40)                                                                      APS                                       10   H  H(80)                                                                              H  H     H(10)                                                                              AMMPS.sup.6 (10)                                                                       ABDV                                      __________________________________________________________________________     .sup.1 Ethyl acrylate (EA)                                                    .sup.2 Diallyldimethyl ammonium chloride (DADMAC)                             .sup.3 Methacrylamidopropyltrimethyl ammonium chloride (MAPTAC)               .sup.4 Acrylamidopropyltrimethylammonium chloride (APTAC)                     .sup.5 Dimethylaminoethylmethacrylate/methyl chloride quaternary.             (DMAEMMC)                                                                     .sup.6 2Acrylamido-2-methylpropane sulfonic acid                         

EXAMPLE 11

The copolymer of Example 1 is evaluated with a South American copperconcentrate which contains 0.8% Mo. The standard depressant is sodiumhydrosulfide. The results are as follows:

    ______________________________________                                                                Copper  Mo      Mo                                             Dosage         Recovery,                                                                             Recovery,                                                                             Grade,                                Depressant                                                                             Kg/Ton         %       %       %                                     ______________________________________                                        NaSH (100%)                                                                            2.4            5.13    95.18   9.4                                   Copolymer                                                                              0.19                                                                 of Example 1                                                                  (28.3%                  3.23    96.14   13.20                                 Active) plus                                                                  NaSH (100%)                                                                            0.52                                                                 ______________________________________                                    

The copolymer of Example 1 gives equal or better Mo recovery and Mograde but lower copper recovery showing its efficacy as a copperdepressant. The over-all NaSH consumption is reduced from 2.4 Kg/Ton to0.52 Kg/Ton and the actual copolymer usage is merely 0.19×0.283=0.054Kg/Ton!

EXAMPLES 12-20

Following the procedure of Example 11, the polymers of Examples 2-10 areused to depress Cu and float Mo. In each instance the results aresimilar to those achieved in Example 11. Use of the polymers of Examples1-11, in the absence of the surface modifying agent, i.e, NaSH, alsoresults in a satisfactory separation of Cu and Mo.

It must also be noted that the dosages of the novel polymer and NaSH inExample 11 are not optimized. Those skilled in the art will be able toreadily obtain the best performance at very low dosages of the novelpolymer by simply optimizing the dosages of the polymer, alone, or withNaSH. Although it is not our objective to be bound by any one mechanismfor the efficacy of the combination of the novel polymer and NaSH inCu-Mo separation, one could speculate that the role of the small amountof NaSH used in Example 11 is one of activating/cleaning the Cu sulfidemineral surfaces, so that the novel polymer can adsorb on theseselectively rather than on MoS₂ surfaces. Stated differently, the novelpolymer adsorbs effectively and selectively on Cu sulfides underappropriate redox potentials NaSH, being a strong reducing and potentialdetermining agent for sulfides, is providing such appropriate redoxconditions at controlled dosages One can also speculate that if theconditions are too reducing (i.e., very high dosages of NaSH), theadsorption of the novel polymer would be destabilized in a mannersimilar to the destabilization of the xanthate collectors Under theseconditions, as also in the absence of NaSH, the polymer would beadsorbed non-selectively on MoS₂ surfaces, though this adsorption isweak and physical in nature.

It must be noted that any other chemical with strongly reducing oroxidizing (in certain minerals systems) properties can be used inconjunction with the novel polymer to obtain appropriate redoxconditions. In other words, any "surface-modifying" agent can be used toprepare the sulfide surfaces to enhance adsorption of the novelpolymers. Examples of such reagents include NaCN, Nokes reagent,mercaptoethanol, thioglycolic acid, Na or K ferri and ferro cyanides,hydroxyethyltrithiocarbonates, and other trithiocarbonates, hydrogenperoxide, ozone, air, oxygen, sulfur dioxide, zinc cyanide, arsenicNokes, mercaptopropionic acid, mercaptosuccinic acid, other relatedmercapto acids, 2-thiouracil, thioglycerol and the like. Additionalcompounds that can be used in conjunction with the novel polymer aregiven in the publication Nagaraj et al., Trans. IMM, Vol. 95, Mar. 1986,pp. C17. Ratios of these surface modifying agents to the novel polymerhereof range from about 0.05-5.0:1, respectively, preferably about0.02-2.0:1, although conditions of use and ores treated may vary theseamounts somewhat.

A further point to note is that a conditioning time of 20 min. isusually required for standard depressants, whereas with the novelpolymer hereof, conditioning times of less than 10 minutes are oftenquite adequate This time differential has a significant practicalimplication in terms of higher throughput and operational cost savings.

We claim:
 1. A polymer composition consisting essentially of recurringunits of the formula: ##STR7## wherein R is hydrogen or a C₁ -C₄ alkylgroup, R¹ and R² are, individually hydrogen, a C₁ -C₄ alkyl group or anaryl group, R³ is hydrogen, a C₁ -C₄ alkyl group or an aryl group, M ishydrogen, an alkali metal ammonium or C₁ -C₄ alkyl ammonium, Zrepresents the polymerization residue of any copolymerizable monomerexcept an acrylamide, x represents a residual mole percent fraction,ranging from about 1.0 to about 49.0%, by weight, based on the totalweight of x, y and z, z represents a mole percent fraction ranging fromabout 0% to about 49.0%, same basis, and the molecular weight of thepolymer is between about 1,000 and about 1,000,000 and asurface-modifying agent.
 2. A composition according to claim 1 whereinsaid surface-modifying agent is NaSH, NaCN, Nokes reagent, mercaptoethanol, thioglycolic acid, sodium and potassium ferrocyanides andferricyanides, hydroxyethyltrithiocarbonates, carboxyethyltrithiocarbonates, sodium trithiocarbonates, hydrogen peroxide, ozone,air, oxygen, sulfur dioxide, zinc cyanide, calcium cyanide, arsenicNokes, mercapto propionic acid, mercapto succinic acid, 2-thiouracil orthioglycerol.